Got the following in my vagrant system. Reloading the page succeeded.

Fatal error: Call to a member function real_escape_string() on a non-object in includes/db/DatabaseMysqli.php on line 187

Call Stack: 0.0067 642016

1. {main}() index.php:0
2. MediaWiki->run() /vagrant/mediawiki/index.php:49
3. MWExceptionHandler::handle() includes/Wiki.php:470
4. MWExceptionHandler::report() includes/Exception.php:678
5. MWException->report() includes/Exception.php:606
6. DBConnectionError->reportHTML() includes/Exception.php:259
7. MWException->reportHTML() includes/db/DatabaseError.php:222
8. DBConnectionError->getPageTitle() includes/Exception.php:225
9. DBConnectionError->msg() includes/db/DatabaseError.php:148
10. Language->getMessage() includes/db/DatabaseError.php:129
11. LocalisationCache->getSubitem() languages/Language.php:2337
12. LocalisationCache->loadSubitem() includes/cache/LocalisationCache.php:281
13. LCStore_DB->get() includes/cache/LocalisationCache.php:379
14. DatabaseBase->selectRow() includes/cache/LocalisationCache.php:1097
15. DatabaseBase->select() includes/db/Database.php:1585
16. DatabaseBase->selectSQLText() includes/db/Database.php:1494
17. DatabaseBase->makeList() includes/db/Database.php:1546
18. DatabaseBase->addQuotes() includes/db/Database.php:1966
19. DatabaseMysqlBase->strencode() includes/db/Database.php:2366
20. DatabaseMysqli->mysqlRealEscapeString() includes/db/DatabaseMysqlBase.php:455

Version: unspecified
Severity: normal